Electric furnace for producing oxids of phosphorus from natural phosphates.



i P. s. WASHBURN. v v mOTH-IQPURNACE FORPBODHGING OXIDS 0F PHOSPHORUS PROM NATURAL PHOSPHATES. APPLIOATION FILED JUNE 17, 1912.

I Patented Nov.19,1912.

' To all whom it may concern:

FRANK 3. WASHBURhT, F NASHVILLE, TENNESSEE.-

EL ZEC'IR IIC FURNACE PRODUCING OXIDS 0F PHOSPHORUS FROM NATURAL PHOSPHATES.

' Application filed June 17,

Be it known that I, FRANK S. WAsnLBURN, a citizen of the United States, residing at Nashville, in the county of Davidson and State of Tennessee, have invented certain new and useful Improvements in Electric Furnaces fdr Producing Oxids of Phosphorus fromv Natural Phosphates; and I do hereby declare the fllowing to be a full,

clear, and exact description of the invention,

such as will enable others skilled in the art to which it appertains to make and use the same.

I This invention relates to an electric furnace especially adapted for separating the phosphorus contained in natural phosphates from-the mineral, a'nd'has for its object to produce an apparatus which will separate this phosphorus in a gaseous form, more quickly and less expensively than the devices heretofore proposed.

To these ends the invention consists in the novel details of construction and co1nbination of parts more fully hereinafter disclosed and particularly pointed out in the claims.

Referring to the. accompanying drawings forming a part of this specification in which the figure is a vertical sectional view of an apparatus built in accordance with my in vention,.-l indicates the hearth of my furnace which may be made of any suitable refractory material,- and 2 the electrodes projecting tlurough the openings 3 which are larger than the said electrodes. Preferably lining the openings 3 are the tubes d-made of any suitable material, and inthe said tubes 4. is preferably placed granular coke 5, or other form of carbon in order to save the consumption of the electrodes 3. This fcoke or carbon is sullicicnlly packed in the tubes 4, to prevent any wasteful escape of gases. In the walls (3 of the furnace 1 provide a plurality of openings 7.for the admission of air to the phosphorus gases given ofi', in order that the phosphorus may be oxidized to the pentoxid form before it escapes from the furnace. The said'openings .7 may, if desired, further be provided with valve controlled pipes 8, in order that the amount of air admitted may be re-ulated, and therefore the degree of oxidation of the phosphorus controlled.

A charge 9 preferably composed of granular coke. silica and mineral phosphate Specification of Letters Patent.

Patented Nov. 19,1912- 1912. Serial no. 704,170.

is introduced to the furnace through the tube 10, which in turn is controlled by the hopper 11 and the bell-shaped valve 12, as shown. The tube 10 extends below the lowest opening 7 as indicated, so that the charge contaii'ie'd therein will'not be subjected to the action of the air entering the opening 7. An annular space 13 is left between the tube 10 and the walls -of the furnace, and a valved pipe 14 for drawing 05 the liberated gases communicates with said space, as shown.

In order that the exact principles in volved in this furnace may be clearly understood, and further, in order that these prin-. ciples may be the more easily differentiated from the prior art, the following well known chemical principles. are stated, as well as the details of certain large scale tests that have been carried on by myself. It is well known that an acid may be displaced. from a salt combination by another less volatile acid. For example, hydrochloric and nitric acids have long since been made from their naturally occurring combinations by displacement with the less volatile sulfuric acid, the hydrochloric and nitric acids being boiled off from the mixture and condensed in suitable towers. 011 these same chemical grounds it should therefore be possible to decompose a natural phosphate by an acid less volatile than phosphoric acid. In such case, thecheapest and most easily obtainable less volatile acid is silicic, found in the form of the anhydrid, $10,, which does not volatilize much under 1800 C. in. its pure state. and at even higher temperatures in combination with a strong base. Accordingly, large scale experiments were made to determine if silica would in fact displace phosphoric acid from its combinations at a tcu'iperz' ture above the vola tilizatiou point of the phosphorus peutoxid, and it was found that if a mineral plies-- phatc,for example the tricalcium phosphate la l tl is mixed without carbon with silica as a flux, and subjected to the temperature of an oi'di1iary fur1iace phosphorus peutoxid P 0 will be evolved in small amounts. but never amounting to more than a few per cent. of the total phosphorous conmined in theluixture, even if the heating is sullicient to produce fusion. It was further found that if such a mixture be heated to Fusion in an ordinary furnace in the presence of carbon, a larger yield of phosphorus will be had. Some of this phosphorus was found to be in the form of vapor, while other portions were in the form of a mixture of various oxids of phosphorus. But, after a long series of large scale and expensive tests with various types of furnaces, other than electric furnaces, was had, it be came apparent tliat it was not possible to separate a sufficient quantity of the phos' phorus contained in the mixture, to render the process commercially successful. The cause of this is not at present fully understood, for the addition of carbon to the phosphate undoubtedly weakens the bonds by which the phosphate is bound, and as the mixture can be fused in such furnaces, the

phosphorus should be freely evolved when it is not I Upon employing a furnace of the type illustrated, however, as much as 90% of thecontained phosphorus is immediately driven off, probably due to .the accelerated action of the carbon in loosening the bonds of llllelDliOSPllOItlS at the higher temperatures available,and also probably due to the greater fluidity of the molten bath 16 at such temperatures. l Vhatever may be the real cause, such a furnace, in fact, supplies a means by which a commercia process can be carried out.

The operation of my furnace is as follows :-The charge of finely divided 'phos phate, silica and coke, preferably chemically proportioned with the carbon slightly in excess, is continuously fed down the tube 10, and the current turned on. The molten material collects on the hearth 1, and may be drawn out of the tap hole 18 from time to time. As above stated, sul'istantially all of the phosphorus contained in the mixture is quickly evolved, and the gases pass up through the charge above the fusion zone, and become mixed with the air admitted through the openings 7. The phosphorus in suit gases thereupon lKBCOHlCS readily oxidized to the pentoxid t'orm P 0 while the heat thus liberated passes through the walls of the tube 1) and serves to preheat the dcscendiug charge. 'lhc oxidized phospl'iorus with the other gases is withdrawn by way of the tube. l-it to a suitable apparatus, not shown, which separates out the phosphorus bearing gases, in the manner well known. It will be observed that the air admitted through the openings 7 to oxidize the phosphorus does not pass through the charge containing carbon in the tube 10, andtheretore no loss is experienced through the oxidation of said carbon, which would otherwise occur. It will be further observed, should itbe desired to otherwise utilize the heat liberated by the oxidation of the phosphorus", that the tube 10 may be made suiticiently thiclcto prevent any substantial transmission of said heat to its contained charge, and in that case the heat may he carried out of the furnace either by the hot gases or by other means. 'It Will be further observed that the construction illustrated permits the employment of charges in a fine state of division without necessitating a high gas pressure in the furnace, or on the fusion zone, because the gases must only pass through a comparatively thin layer of the charge material before entering the annular space 13, and theymay be continuously.

drawn ofl from said space formed.

What I claim is:-

1. An electric furnace provided with a tight chamber; a hearth at thebottom of said chamber; lectrodes passing into said as fast as chamber provided with a granular carbon" parking also entering said chamber; a valved feed tube extending into said chamher and terminating above said hearth; and

means entering said chamber above the' lower end of said tube for admitting air to said chamber for oxidizing the evolved gases, substantially as described.

2. An electric furnace provided with a gas tight chamber; a hearth at the bottom of said chamber; electrodes passing into said chamber provided with a granular carbon packing also entering said chamber; tubes surrounding said electrodes for bold ing said packing; a valved feed tube extending into said chamber and terminating above said hearth adapted to deliver a charge of finely divided phosphate rock, silica and carbon to said hearth; means entering said chamber above 'the'lower end oi. said tube for admitting air to said chamber for oxidizing the evolved gases without igniting the carbon in said tube; and means for continuously withdrawing the oxidized gases from said chamber, substantially as described.

In testimony whereof,I afiix my signature, in presence of two Witnesses.

. FRANK S. NBSHBURII.

Witnesses BLACK, :IRKPA'IRIGR. 

